The present invention relates to adapting a control strategy for an automated transmission of a heavy commercial vehicle based on the active/inactive state of an imposed power take offload.
Heavy commercial vehicles such as overland trucks and buses are known to employ automatic manual transmissions (AMT) that are based on preprogrammed routines. One of the problems in controlling an AMT, however, is attributable to the power consumption by a power take off (PTO). A PTO can typically be classified as a PTO upstream or downstream of the master clutch. In general, a PTO that is upstream of the master clutch can take power from the vehicle's engine regardless of the state of engagement of the transmission via the master clutch. A PTO that is located downstream of the master clutch is typically used when the vehicle is stationary. Use of a downstream PTO often involves placing the gearbox in neutral so that the vehicle wheels are not drivingly engaged to the transmission. However, there are cases when a downstream, transmission mounted PTO is used while the vehicle is in motion.
PTOs are known to impose significant load on the vehicle's engine. Exemplary PTOs use engine power to drive hydraulic pumps that can be activated for such things as mixing applications (concrete trucks) or causing motion of a bed on the truck such as in the case of dump trucks and flat-bed haulers.
Similarly, PTOs may be used to power spreaders such as those used to broadcast salt or sand on icy roads, or to power associated trailer components such as compartment refrigeration units. While these examples are not exhaustive, they do serve to exemplify PTO loads of significant magnitude which can appreciably compromise the driving power available from the engine for the drive wheels, and which often causes undesirable disturbances to automated transmission programs that do not take their intermittent influences into account. For purposes of comparison, these significant PTO loads can be compared to less influential engine loads imposed by such power consumers as cooling fans and air conditioning compressors. As an example of the potential drag that a PTO can impose on the vehicle's engine, it is not uncommon for PTOs to siphon off engine torque on the order of 5 to 3000 Nm. An example of a PTO that requires on the order of 3000 Nm is a fire truck that operates a water pump and an example of a PTO that requires on the order of 5 Nm is the drag imposed by a small refrigeration device.
The present invention appreciates the fact that transmission control routines that do not take into consideration whether or not a significant PTO load is imposed on the vehicle's engine will experience degradation in performance when the PTOs are operational. For example, if the PTO loads are of such magnitude that the engine can not compensate therefore by increased engine speed, there will be an effective reduction in power available for driving the vehicle. The strategy must, however, appreciate that the behavior of the PTO-loaded engine is not that of a smaller engine, but is in fact a unique behavior of the particular engine whose power is divided between a PTO of significant drag and the drivetrain.
Still further, it has been appreciated that it can be difficult to adjust a transmission when the PTO is engaged while the vehicle is in motion; therefore, one of the aspects of the present invention has as a goal to provide a solution where downshift information is used to adapt the transmission controls. When the engine is enabled to supply a certain amount of torque to the driveline, an increase in engine speed is expected when the master clutch is disengaged. With a PTO engaged, the engine speed increases when the master clutch is disengaged, but the magnitude of the increase in engine speed is less than the increase in engine speed without a PTO load. Thus, it is desirable to consider the additional load of the PTO when programming gear shifting strategies.
This can be contrasted to the solution of U.S. Pat. No. 5,582,069 in which PTO load detection is limited to up-shift situations where engine deceleration is analyzed when the gears are decoupled for an up-shift to a lower gear ratio engagement and the engine is defueled. The disclosure of U.S. Pat. No. 5,582,069 is expressly incorporated herein by reference in its entirety.
The present invention has two primary heretofore unrealized functions, with associated benefits. The first is the manner in which it is determined whether the PTO is operating. This is accomplished by comparing torque that is available to power the drive wheels of the vehicle to a total torque that is being generated by the engine. When the difference is greater than a nominal amount, that difference approximates the torque attributable to the PTO's activity. In practice, a nominal amount of torque consumption must be allowed for such things as engine friction loss, oil pumps, air-conditioning compressors and the like. These torque consumption amounts, however, will be substantially smaller than that of a PTO for carrying out such activities as cement mixing, bed dumping or garbage compaction. The primary benefit of using this manner for determining the presence of an active PTO load is that it can be measured at essentially anytime the engine of the vehicle is operating, and is not limited to such narrow time frames as in U.S. Pat. No. 5,582,069 where PTO load detection is limited to up-shift situations in which the gears are decoupled and the engine is defueled.
The second primary new function of the presently disclosed method and arrangement is the fact that certain gear-shift events are controlled to occur at higher engine speeds when it is detected that the PTO is operating. The primary events include, but are not limited to up-shifts and down-shifts. The underlying concept is that the PTO is consuming a certain amount of torque that at the particular engine speed would otherwise be available for engine acceleration. Therefore, the engine speed is increased an amount that compensates for the PTO's torque consumption. This is important in an up-shift event were the vehicle operator will want approximately the same amount of available drive wheel acceleration after the shift is completed whether or not the PTO is functioning. In this way, the claimed method and arrangement helps to make the existence of the PTO and its working state more transparent to the driver. Where possible, the performance of the vehicle will be maintained because the engine speed at which the up-shift occurs is higher when the PTO is operating. This is also important in a down-shift event where the engine must be sped up for engaging the higher ratio gear when the gear-shift is completed. As before, upon completion of the gear shift, the operator will want similar responsiveness; i.e. drive wheel acceleration responsiveness regardless of whether or not the PTO is engaged. Therefore, here again, the speed of the engine at which the down-shift event occurs is commensurately adjusted upwardly when the PTO is active.
In summary, the solutions of the present disclosure enjoy benefits over known methods and arrangements in that the operational state of the PTO can be assessed when in the power mode and the result is an upward adaptation of the engine speed at which certain gear-shift events are affected.